Effects of nutrition, oxidation, and other environmental factors (light intensity or darkness) on incidence and progress of posterior subcapsular opacities (PSO) associated with genetically influenced retinal degeneration are being studied in pink-eyed Royal College of Surgeons (RCS) rats, in which rod photoreceptor outer segment debris accumulates secondary to a phagocytic defect in retinal pigmented epithelium (RPE). Peroxidation in polyunsaturated fatty acids in debris led to water- soluble toxic aldehydes, detectable in the vitreous and toxic to lens cells and membranes. Dystrophic rats fed a natural ingredient diet (NIH- 07) were highly sensitive to retina light damage, beginning at an intensity of 1-4 footcandles (FC), and 27% of the rats developed mature cataracts by 5-12 months. Rhodopsin bleaching is essential for retina light damage and PSO. In vitro, free retinaldehyde has been shown to be a photosensitizer to generate singlet oxygen, an extremely damaging oxidant for both lipids and proteins, and this also occur in vivo. A study of effects of environmental lighting on incidence of bilateral mature cataracts in pink-eyed RCS rats fed the natural ingredient diet (NIH-07) has been completed. Incidence of bilateral cataracts was 5% in rats reared in 1-4 FC of cyclic light but was 25% in rats reared in 10 FC constant light, 70% in 25 FC constant light, and 100% in 65-day-old rats given high-intensity (700 FC) for 48 hours. In RCS rats reared at 1-4 FC, a purified diet (AIN-76A) fortified with antioxidants (0.4% beta-carotene + 0.01% BHT) prevented PSO and mature cataracts. Currently a diet containing additional antioxidants (1,000 mg/kg diet of vitamin C and 150 mg/kg vitamin E) retarded retinal degeneration during the time the concentrations of vitamin E has been completed, but the histopathological evidence in the retina has not been evaluated.